Secretion of anterior pituitary hormones undergoes feedback control by peripheral hormones secreted from target organs of the respective hormones and by secretion-regulating hormones from the hypothalamus, which is the upper central organ of the anterior lobe of the pituitary (hereinafter, these hormones are collectively called "hypothalamic hormones" in this specification). At the present stage, for hypothalamic hormones, the existence of nine kinds of hormones including, for example, thyrotropin releasing hormone (TRH), and gonadotropin releasing hormone [GnRH, sometimes called LH-RH (luteinizing hormone releasing hormone)] has been confirmed. These hypothalamic hormones are believed to show their actions via the receptors which are considered to exist in the anterior lobe of the pituitary, and efforts to find the receptor-gene expression specific to these hormones, including for humans, have been made. Accordingly, antagonists or agonists specifically and selectively acting on these receptors should control the action of the hypothalamic hormone and the secretion of anterior pituitary hormone. As a result, such antagonists or agonists are expected to be useful in preventing treating anterior pituitary hormone diseases.
Known compounds possessing GnRH-antagonizing activity include GnRH-derived linear peptides (U.S. Pat. No. 5,140,009 and U.S. Pat. No. 5,171,835), a cyclic hexapeptide derivative (JP-A-61-191698), a bicyclic peptide derivative [Journal of Medicinal Chemistry, Vol. 36, pp. 3265-3273 (1993)], and so forth. Non-peptide compounds possessing GnRH-antagonizing activity include compounds described in WO 95/28405 (JP-A-8-295693), WO 97/14697 (JP-A-9-169767), WO 97/14682 (JP-A-9-169735) and WO 96/24597 (JP-A-9-169768), etc.
Peptide compounds pose a large number of problems to be resolved with respect to oral absorbability, dosage form, dose volume, drug stability sustained action, metabolic stability etc. There is strong demand for an oral GnRH antagonist, especially one based on a non-peptide compound, that has excellent therapeutic effect on hormone-dependent cancers, e.g., prostatic cancer, endometriosis, precocious puberty etc., that does not show transient hypophysial-gonadotropic action (acute action) and that has excellent bioavailability.